Polyolefin polymers and polymer blends are known for their versatility and applicability in a wide variety of uses. In particular, many polyolefin polymers, including copolymers of propylene with other α-olefins such as ethylene, are well suited for use in applications requiring good stretchability, elasticity, and strength. Materials with good stretchability and elasticity are used to manufacture a variety of disposable articles in addition to durable articles including but not limited to incontinence pads, disposable diapers, training pants, clothing, undergarments, sports apparel, automotive trim, weather-stripping, gaskets, and furniture upholstery. For clothing, stretchability and elasticity are performance attributes that allow the materials to provide a closely conforming fit to the body of the wearer.
While numerous materials are known to exhibit excellent stress-strain properties and elasticity at room temperatures, it is often desirable for elastic materials to provide a conforming or secure fit during repeated use, during extensions and retractions at elevated or depressed temperatures, or in automobile interiors during summer months. Elasticity at elevated temperatures is also important for maintaining tight tolerances throughout temperature cycles. In particular, elastic materials used for repeated wear clothing or garments must maintain their integrity and elastic performance after laundering.
Spandex, a segmented polyurethane urea elastic material, is currently used in various durable fabrics. For example, fibers made from Spandex have been used in launderable apparels, fabrics, durable and disposable furnishing, beddings, etc. Similar to conventional uncrosslinked polyolefin-based elastic materials, articles made from Spandex can lose integrity, shape, and elastic properties when subjected to elevated temperatures. Thus, Spandex is not suitable for many co-knitting applications with high temperature fibers, such as polyester fibers.
Many polyolefin blends such as those disclosed in the prior art are formed into pellets for intermediate storage purposes before being shaped into articles such as fibers, films, nonwovens, extruded coatings, and molded articles. Some of these compositions, however, are known to exhibit poor pellet stability over extended periods of time, leading to agglomeration of pellets and resulting in poor pourability and flowability of the pellets. U.S. Pat. No. 8,975,334 discloses the process of making a crosslinked article from a propylene-based composition to address some of these limitations, using peroxide. Conventional grafting processes generally disclose using chemical agents, such as peroxide. However, the inclusion of peroxide may lead to formation of gels, making it difficult to fabricate continuous aesthetic parts in some applications.
Accordingly, there is still a need for new and improved propylene-based materials which exhibit good pellet stability while also displaying good stretchability and elasticity for use in a wide variety of applications with reduced tendency to form a gel during the grafting process.